On Tue, Nov 01, 2016 at 07:19:59AM -0700, Eric Dumazet wrote: > On Tue, 2016-11-01 at 00:57 +0200, Ido Schimmel wrote: > > On Mon, Oct 31, 2016 at 02:24:06PM -0700, Eric Dumazet wrote: > > > > How well will this work for large FIB tables ? > > > > > > Holding rtnl while sending thousands of skb will prevent consumers to > > > make progress ? > > > > Can you please clarify what do you mean by "while sending thousands of > > skb"? This patch doesn't generate notifications to user space, but > > instead invokes notification routines inside the kernel. I probably > > misunderstood you. > > > > Are you suggesting this be done using RCU instead? Well, there are a > > couple of reasons why I took RTNL here: > > > > No, I do not believe RCU is wanted here, in control path where we might > sleep anyway. > > > 1) The FIB notification chain is blocking, so listeners are expected to > > be able to sleep. This isn't possible if we use RCU. Note that this > > chain is mainly useful for drivers that reflect the FIB table into a > > capable device and hardware operations usually involve sleeping. > > > > 2) The insertion of a single route is done with RTNL held. I didn't want > > to differentiate between both cases. This property is really useful for > > listeners, as they don't need to worry about locking in writer-side. > > Access to data structs is serialized by RTNL. > > My concern was that for large iterations, you might hold RTNL and/or > current cpu for hundred of ms or even seconds...
I understand your concern, but I think it's helpful to look at the users of this API. It was only recently introduced [1] because nobody needed it beside switch drivers that reflect the FIB table and I believe it'll stay that way. Currently, only mlxsw and rocker use it. Now, in these use cases when register_fib_notifier() is called the switch ports are still not present in the system, so we really only have a few routes used for management. Similarly, when unregister_fib_notifier() is called, the switch ports are already gone and most FIBs were flushed due to NETDEV_UNREGISTER, so again we only have a handful of FIBs to iterate over. Does that sound reasonable to you? 1. https://www.spinics.net/lists/netdev/msg397444.html
